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HS VS HSS
Elinchrom's Skyport Transmitter Plus HS has opened a new world of High-Sync photgraphy to many users. But, what is Hi-Sync, and which flash units will it work with?....
The first thing we should clear up is the difference between HSS and Hi-Sync, because they are not the same.
In fact, no, the first thing we need to do is explain WHY we need these things at all...
As I hope you know, inside your camera is a shutter, it consists of 2 metal blades which cover the chip (or film if that's your thing.) When you take a picture one of the blades moves accross to uncover the sensor. After the required exposure time, the second blade follows the first and re-covers the chip. Both blades then re-set to the original position.
As the shutter speed (or more accurately exposure time) gets faster, there's a point at which the second blade starts moving before the first blade has reached the other side. At this point the whole chip is never exposed in one go. This means that there isn't a point at which you can fire a flash and have it expose the whole frame.
As the exposure time decreases the slit gets narrower and narrower.
So, in theory, there's no way to use a flash above the speed at which the whole chip is exposed. This speed is often called the camera's flash sync speed, or x sync speed.
But we can sync at high shutter speeds, how does that work?
HSS, short for High Speed Sync (also known as FPSync in the Nikon world) is a technology used originally in speedlights but now also in larger flash units. It uses the ability of a speedlight to flash at a very high frequency (but at a very low power). Essensially the flashgun continuously flashes as the slit in the shutter moves accross the frame. This give a nice even illumination, but, because each flash is so low power, it isn't suitable for overpowering bright ambient light (unless you gang together a lot of speedlights).
But each flash is very small.
So, how do we get more power?
Hi-Sync (or Hypersync, ODS, long-tail flash etc...) makes use of the fact that a flash is not instantaneous. Although to our eyes a flash looks like it takes no time it in fact has a complex brightnes curve as it is triggered, comes to a peak brightness and then tails off. By timing the peak of the flash to co-incide with the shutter and selecting a flash unit with a peak in the curve long enough to cover the shutter travel, we can in effect turn the flash into a continuous light source.
This is what the ODS setting on the Skyport HS Transmitter is for.
This is what the Quadra HS head does.
So what advantage is there in Hi-Sync over HSS?
Because Hi-Sync used the peak of the flash, rather than lots of low power flashes, it gives you a higher output. This makes it more suited for 'fighting the sun'. It also doesn't require a special flash unit. Having said that, Hi-Sync works better with longer flash durations, and the Elinchorm Quadra HS head has a flash duration especially tuned to make H-Sync work well.
So Which heads can I use?
The table below shows the results from using Hi-Sync with a range of Elinchrom products. They are cropped form a larger image but show the important top-bottom gradient. The images were shot on a 1DX which syncs normally at ~ 1/250s. ISO was kept at 100 but aperture was varied in each sequence to keep the overall exposure roughly the same.
All units were fired at full power, reducing power will lengthen the flash duration and improve the gradient but with a corresponding lower exposure.
The important feature we're trying to highlight is the gradient.
| Speed | Quadra HS Head |
D-Lite RX4 | Ranger with S Head |
Quadra Pro head> |
Quadra Action Head |
|---|---|---|---|---|---|
| 1/125s |
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| 1/250s |
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|
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| 1/500s |
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| 1/1000s |
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| 1/2000s |
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| 1/4000s |
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 |
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| 1/8000s |
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|
As you can see the Quadra HS head creates images with the smallest gradient, and this is due to it's extremely low flash duration of 1/550s at full power. Whilst the Quadra Pro Head (1/1200s) is very useable across the sync range (depending on your specifc requirements) the Quadra Action Head struggles to create a consistent frame anywhere faster than a sync speed of 1/1000s. This is due to the Action heads fast flash duration of 1/2800s. With this in mind it is fair to assume that all other Elinchrom heads with a flash duration over 1/2000s will experience the same issues, including BRX / BXRi, Style 300 & 600 RX, D-Lite RX One and ELC Pro HS Heads. For the best results with an Elinchrom mains powered unit, we recommend the D-Lite RX 4 Head.
For information, we've also included results with the Ranger Pack with S Head. At full power as shown, this flash setup does create some gradation in the images due to it's flash duration of 1/1160s. However, with the power knocked down a little and the flash duration shortened, Hi-Sync results with this head are fairly good.
Which other features of the Skyport transmitter HS can I use with my existing kit?
The list of which features work on which heads is pretty complex,you can find the most up-to-date version here.
2021 UPDATE -
Elinchrom now has a range of flash units available that utilise HSS.
The ELC TTL range are mains power, come in 125Ws or 500Ws variants and include TTL as well as HSS. This means that you can have fully automatic flash power control (should you want to, it can always be set to manual!) and shoot at the highest speeds available on your camera.
The Elinchrom ONE is a new battery powered head that gives you the features of a studio flash, AND a speeedlight, on location. It's light, portable, has TTL and HSS, an LED modelling lamp and ships with an adapter to utilise your existing Elinchrom accessories.